Ecosystems

Chapter 54

• Ecosystem involves all abiotic and biotic factors in area.

• Trophic levels - groups in which organisms are placed according to eating patterns.

• Ecosystems - involve nutrient cycles.

http://www.oahunaturetours.com/pelagic/images/sbbfoodchain1.GIF

• Autotrophs - self-feeders (usually photosynthesize) -primary producers

• They use light to make sugars, other chemicals necessary for life.

http://static.howstuffworks.com/gif/irrigation-photosynthesis.gif

• Heterotrophs - rely on organisms for food.

• Herbivores – eat primary producers (primary consumers)

• Carnivores - eat primary consumers (secondary consumers)

• Tertiary consumers - eat secondary consumers.

• Detritivores - decomposers - break down detritus (dead organic matter left after organism dies)

• Organic matter must be recycled in ecosystem.

• Biggest decomposers - fungi and prokaryotes (secrete enzymes to break down dead material)

• Primary production - amount of light that can be converted to energy in a given time.

• All contributes to energy budget in an area (determines how much energy available to ecosystem)

http://adaptation.nrcan.gc.ca/posters/images/pr_02_01_e.gif

• Gross primary productivity - amount of light energy converted to chemical energy.

• Net primary productivity - gross productivity minus amount of energy used by primary producers for respiration (amount of energy left over)

http://eostc.umt.edu/forestry/Products/Production/Forest%20Production/first_modis_gpp.gif

• Primary production - expressed in terms of biomass (amount of vegetation added to ecosystem per unit area per unit time)

• Each ecosystem different amount of biomass.

• Oceans - amount of light to hit ocean floor contributes biomass.

• Light can only go to certain level; primary productivity of area may be lower in deeper oceans.

Primary Productivity Map

• Nutrients also contribute to biomass in aquatic areas.

• Nitrogen - plant growth (can be limited in water)

• Water pollution adds nutrients to water (eutrophication)

• Shifts organisms living in water and is a negative impact of humans.

Eutrophication of lake

• Land areas - temperature and water availability also determines primary productivity.

• Minerals in soil can affect production as well.

http://www.usf.uni-osnabrueck.de/~hlieth/npp/npp.gif

• Efficiency between trophic levels is at best 20%.

• Transfer from one level to next is only 20% of energy from level before.

• Biomass pyramids show transformations between trophic levels.

• Differ dramatically between ecosystems.

• Nutrient cycling involves abiotic and biotic factors (biogeochemical cycling)

• Water cycling physical cycle and not chemical; not considered biogeochemical cycle, but still essential to ecosystem.

Carbon cycle is a biogeochemical cycle.

• Nitrogen enters an ecosystem in 2 ways.

• Added to soil in usable form.• Can also enter through nitrogen

fixation - prokaryotes convert nitrogen into usable organic compounds like amino acids.

• Product of nitrogen fixation is ammonia.

• Ammonia picks up H+ in soil to become ammonium (ammonification)

• Plants can use this nitrogen.• Aerobic bacteria can turn

ammonium into a nitrate (nitrification)

http://www.thisland.uiuc.edu/50ways/images/5b.jpg

• Nitrates - used by plants.• In final step, other bacteria use

oxygen from nitrates and release N2 back into atmosphere (denitrification)

http://generalhorticulture.tamu.edu/lectsupl/Nutrient/p79f1.gif

• Phosphorus occurs only in phosphate - plants absorb and use to make organic nutrients.

• Does not come from atmosphere.• Recycling of phosphorus is

usually confined to specific areas.

• Rate of decomposition determines rate of chemical cycling.

• Tundra - decomposition can take years; rain forest - decomposition takes much less time.

http://farm1.static.flickr.com/221/507417180_dfd8f5e8ac.jpg?v=0

• Humans affect rate of chemical cycling due to habits.

• Farmers - disturb crop areas by removing nutrients in soil.

• Humans - add fertilizers to soil which disrupt chemical balances.

• Chemicals can enter water, disrupting animals that live there.

• Burning of fossil fuels - major contributors to nutrients in atmosphere.

• Sulfur and nitrogen placed into atmosphere change into acid precipitation.

Acid precipitation

• Acid precipitation can alter pH of soil and alter the vegetation that lives there.

• Poisonous materials also added to our soils and water.

• Further up food chain, more organism is affected by chemicals.

• DDT (a pesticide) damaged birds and fish when it met with water.

• Amount of carbon dioxide in atmosphere has been rising for decades.

• Carbon dioxide helps to keep in heat that would normally escape atmosphere (greenhouse effect)

• Ozone layer is thinning as a result of fossil fuels.

• Ozone protects humans from UV rays.